GM Service Manual Online
For 1990-2009 cars only
Makes 🢒 Chevrolet 🢒 2001 🢒 Impala 🢒 Restraints 🢒 SIR 🢒 Scan Tool Does Not Communicate with Class 2 Device

Circuit Description

Modules connected to the class 2 serial data circuit monitor for serial data communications during normal vehicle operation. Operating information and commands are exchanged among the modules. Connecting a scan tool to the DLC allows communication with the modules for diagnostic purposes. Diagnostic trouble codes (DTCs) may be set due to this symptom and during this diagnostic procedure. Complete the diagnostic procedure in order to ensure all the DTCs are diagnosed and cleared from memory.

Diagnostic Aids
    • The BCM detects that the ignition is ON and sends the appropriate power mode message to the other modules. The BCM must be connected to the class 2 serial data circuit for many other modules to communicate with the scan tool.
    • If the class 2 serial data circuit was shorted to ground, U1300 or U1305 will be set as history DTCs. Refer to DTC U1300 or DTC U1305 .
    • If the class 2 serial data circuit was shorted to B+ U1301 or U1305 will be set as history DTCs. Refer to DTC U1301 or DTC U1305 .

Test Description

The numbers below refer to the step numbers on the diagnostic table.

  1. A partial malfunction in the class 2 serial data circuit uses a different procedure from a total malfunction of the class 2 serial data circuit. The following modules communicate on the class 2 serial data circuit:

    2. • Auxiliary Power Drop Connector
    • BCM
    • DIC
    • EBCM
    • IPC
    • PCM
    • Radio
    • Remote Playback Device-CD Player (if equipped with UQ3)
    • SDM
    • Vehicle Interface Unit (VIU) (if equipped)

  2. The following DTC's may be retrieved with a history status, but are not the cause of the present condition:

    3. • U1300
    • U1301
    • U1305

  3. A State of Health DTC with a history status may be present along with a U1000 or U1255 having a current status. This indicates that the malfunction occurred when the ignition was ON.

    4.

  4. Data link connector terminals 2 and 5 provide the connection to the class 2 serial data circuit and the signal ground circuit respectively.

    5.

  5. A poor connection at the DLC terminal of the star connector would cause this condition but will not set a DTC.

    6.

  6. An open in the class 2 serial data circuit between the DLC and star connector will prevent the scan tool from communicating with the modules. This condition will not set a DTC.

    7.

  7. The class 2 serial data circuit is shorted to voltage or ground. The condition may be due to the wiring or due to a malfunction in one of the modules. When testing the wire for a short, make sure there is not a module connected to the wire being tested. This test isolates the BCM class 2 serial data circuit.

    8.

  8. The BCM detects that the ignition is ON and sends the appropriate power mode message to the other modules. Therefore, the BCM must remain connected to the DLC for the other modules to communicate with the scan tool. This test isolates the PCM class 2 serial data circuit.

    9.

  9. If there are no current DTCs that begin with a "U", the communication malfunction has been repaired.

    10.

  10. The communication malfunction may have prevented diagnosis of the customer complaint.

Step

Action

Yes

No

1

Does the scan tool power up?

Go to Step 2

Go to Scan Tool Does Not Power Up

2

  1. Turn ON the ignition leaving the engine OFF.
  2. Attempt to communicate with each module on the class 2 serial data circuit. (If using a Tech 2, obtain this information using the Class 2 Message Monitor feature.)

Does the scan tool communicate with any module on the class 2 serial data circuit?

Go to Step 3

Go to Step 9

3
  1. Select the Display DTCs function for each module. (If using a Tech 2, use the Class 2 DTC Check feature in order to determine which modules do have DTCs set.)
  2. Record all of the displayed DTCs, the DTC status and the module which set the DTC.

Did you record any DTCs in the range of U1000 to U1305?

Go to Step 6

Go to Diagnostic Aids

4

Are the DTCs U1300, U1301 or U1305 retrieved from any module?

Go to Step 5

Go to Step 6

5

Important: Turn ON the ignition, with the engine OFF, when testing for a short to voltage. Use the DMM MIN/MAX function to capture intermittent conditions.

Test the class 2 serial data circuit for an intermittent short to ground or an intermittent short to voltage. Refer the following in Wiring Systems:

    •  Circuit Testing
    •  Connector Repairs
    •  Wiring Repairs

Go to Step 31

Go to Step 6

6

Is U1000 or U1255 the only DTC displayed in the previously specified range?

Go to DTC U1000 and U1255

Go to DTC U1001-U1254

7

  1. Turn OFF the ignition.
  2. Disconnect the scan tool from the data link connector (DLC).
  3. Inspect for poor connections at the DLC terminals 2 and 5. Refer to Testing for Intermittent Conditions and Poor Connections and Connector Repairs in Wiring Systems.

Did you find and correct the condition?

Go to Control Module References in Body Control System for the applicable Diagnostic System Check

Go to Step 8

8

Test the DLC ground circuit terminal 5 for an open. Refer to Circuit Testing and Wiring Repairs in Wiring Systems.

Did you find and correct the condition?

Go to Control Module References in Body Control System for the applicable Diagnostic System Check

Go to Step 9

9

  1. Disconnect the star connector.
  2. Inspect for poor connections at the star connector. Refer to Testing for Intermittent Conditions and Poor Connections and Connector Repairs in Wiring Systems.

Did you find and correct the condition?

Go to Control Module References in Body Control System for the applicable Diagnostic System Check

Go to Step 10

10

Test the class 2 serial data circuit for an open or a short between the DLC terminal 2 and the DLC terminal of the star connector . Refer to Circuit Testing and Wiring Repairs in Wiring Systems.

Did you find and correct the condition?

Go to Control Module References in Body Control System for the applicable Diagnostic System Check

Go to Step 11

11

  1. Connect a jumper wire to the DLC terminal of the star connector.
  2. Connect the other end of the jumper wire to the BCM terminal of the star connector.
  3. Turn ON the ignition leaving the engine OFF.
  4. Attempt to communicate with the BCM.

Does the scan tool communicate with the BCM?

Go to Step 13

Go to Step 12

12
  1. Turn OFF the ignition.
  2. Disconnect the BCM.
  3. Test the class 2 serial data circuit between the star connector and the BCM for a short or an open. (Turn ON the ignition leaving the engine OFF when testing for a short to voltage.) Refer to Circuit Testing and Wiring Repairs in Wiring Systems.

Did you find and correct the condition?

Go to Step 31

Go to Step 29

13

  1. Leave the jumper wire connected to the DLC terminal and to the BCM terminal of the star connector.
  2. Connect another jumper wire to the jumper wire connected to the DLC terminal of the star connector.
  3. Connect the other end of the jumper wire to the PCM terminal of the star connector.
  4. Turn ON the ignition leaving the engine OFF.
  5. Attempt to communicate with the PCM.

Does the scan tool communicate with the PCM?

Go to Step 15

Go to Step 14

14
  1. Turn OFF the ignition.
  2. Disconnect the PCM.
  3. Test the class 2 serial data circuit between the star connector and the PCM for a short to ground or a short to voltage. (Turn ON the ignition leaving the engine OFF when testing for a short to voltage.) Refer to Circuit Testing and Wiring Repairs in Wiring Systems.

Did you find and correct the condition?

Go to Step 31

Go to Step 29

15
  1. Disconnect the jumper wire from the PCM terminal of the star connector.
  2. Connect the jumper wire to the auxiliary power drop connector terminal of the star connector.
  3. Turn ON the ignition leaving the engine OFF.
  4. Attempt to communicate with the BCM or VIU (if equipped).

Does the scan tool communicate with the BCM?

Go to Step 17

Go to Step 16

16
  1. Turn OFF the ignition.
  2. Disconnect the auxiliary power connector class 2 serial data circuit.
  3. Test the class 2 serial data circuit between the star connector and the auxiliary power drop connector for a short to ground or a short to voltage. (Turn ON the ignition leaving the engine OFF when testing for a short to voltage.) Refer to Circuit Testing and Wiring Repairs in Wiring Systems.

Did you find and correct the condition?

Go to Step 31

Go to Step 29

17
  1. Disconnect the jumper wire from the auxiliary power drop connector terminal of the star connector.
  2. Connect the jumper wire to the Radio terminal of the star connector.
  3. Turn ON the ignition leaving the engine OFF.
  4. Attempt to communicate with the Radio.

Does the scan tool communicate with the Radio?

Go to Step 19

Go to Step 18

18
  1. Turn OFF the ignition.
  2. Disconnect the Radio.
  3. Test the class 2 serial data circuit between the star connector and the Radio for a short to ground or a short to voltage. (Turn ON the ignition leaving the engine OFF when testing for a short to voltage.) Refer to Circuit Testing and Wiring Repairs in Wiring Systems.

Did you find and correct the condition?

Go to Step 31

Go to Step 29

19
  1. Disconnect the jumper wire from the Radio terminal of the star connector.
  2. Connect the jumper wire to the EBCM terminal of the star connector.
  3. Turn ON the ignition leaving the engine OFF.
  4. Attempt to communicate with the EBCM.

Does the scan tool communicate with the EBCM?

Go to Step 21

Go to Step 20

20
  1. Turn OFF the ignition.
  2. Disconnect the EBCM.
  3. Test the class 2 serial data circuit between the star connector and the EBCM for a short to ground or a short to voltage. (Turn ON the ignition leaving the engine OFF when testing for a short to voltage.) Refer to Circuit Testing and Wiring Repairs in Wiring Systems.

Did you find and correct the condition?

Go to Step 31

Go to Step 29

21
  1. Disconnect the jumper wire from the EBCM terminal of the star connector.
  2. Connect the jumper wire to the SDM terminal of the star connector.
  3. Turn ON the ignition leaving the engine OFF.
  4. Attempt to communicate with the SDM.

Does the scan tool communicate with the SDM?

Go to Step 23

Go to Step 22

22
  1. Turn OFF the ignition.
  2. Disconnect SDM.
  3. Test the class 2 serial data circuit between the star connector and the SDM for a short to ground or a short to voltage. (Turn ON the ignition leaving the engine OFF when testing for a short to voltage.) Refer to Circuit Testing and Wiring Repairs in Wiring System.

Did you find and correct the condition?

Go to Step 31

Go to Step 29

23
  1. Disconnect the jumper wire from the SDM terminal of the star connector.
  2. Connect the jumper wire to the IPC terminal of the star connector.
  3. Turn ON the ignition leaving the engine OFF.

    4. Attempt to communicate with the IPC.

Does the scan tool communicate with the IPC?

Go to Step 25

Go to Step 24

24
  1. Turn OFF the ignition.
  2. Disconnect the IPC.
  3. Test the class 2 serial data circuit between the star connector and the IPC for a short to ground or a short to voltage. (Turn ON the ignition leaving the engine OFF when testing for a short to voltage.) Refer to Circuit Testing and Wiring Repairs in Wiring Systems.

Did you find and correct the condition?

Go to Step 31

Go to Step 29

25
  1. Disconnect the jumper wire from the IPC terminal of the star connector.
  2. Connect the jumper wire to the remote playback device-CD player terminal of the star connector.
  3. Turn ON the ignition leaving the engine OFF.
  4. Attempt to communicate with the remote playback device-CD player (if equipped with UQ3).

Does the scan tool communicate with the remote playback device-CD player (if equipped with UQ3)?

Go to Step 27

Go to Step 26

26
  1. Turn OFF the ignition.
  2. Disconnect the remote playback device-CD player.
  3. Test the class 2 serial data circuit between the star connector and the remote playback device-CD player for a short to ground or a short to voltage. (Turn ON the ignition leaving the engine OFF when testing for a short to voltage.) Refer to Circuit Testing and Wiring Repairs in Wiring Systems.

Did you find and correct the condition?

Go to Step 31

Go to Step 29

27
  1. Disconnect the jumper wire from the remote playback device-CD player terminal of the star connector.
  2. Connect the jumper wire to the DIC terminal of the star connector.
  3. Turn ON the ignition leaving the engine OFF.
  4. Attempt to communicate with the DIC.

Does the scan tool communicate with the DIC?

Go to Step 31

Go to Step 28

28
  1. Turn OFF the ignition.
  2. Disconnect the DIC.
  3. Test the class 2 serial data circuit between the star connector and the DIC for a short to ground or a short to voltage. (Turn ON the ignition leaving the engine OFF when testing for a short to voltage.) Refer to Circuit Testing and Wiring Repairs in Wiring Systems.

Did you find and correct the condition?

Go to Step 31

Go to Step 29

29

Inspect for poor connections at the class 2 serial data circuit of the module that is not communicating. Refer to Testing for Intermittent Conditions and Poor Connections and Connector Repairs in Wiring Systems.

Did you find and correct the condition?

Go to Step 31

Go to Step 30

30

Replace the module which is not communicating. Refer to Control Module References in Body Control System for the appropriate repair instructions.

Did you complete the replacement?

Go to Step 31

--

31

  1. Reconnect all of the disconnected modules.
  2. Reconnect any other disconnected connectors.
  3. Install a scan tool.
  4. Turn ON the ignition leaving the engine OFF.
  5. Wait for 10 seconds.

    6. The scan tool may require a power up reset before communication will occur due to a short on the class 2 serial data circuit. Turn OFF or disconnect the scan tool prior to performing this test.

  6. Select the Display DTCs function for each module. (If using a Tech 2, use the Class 2 DTC Check feature in order to determine which modules do have DTCs set).
  7. Record all of the displayed DTCs and the DTC status.

Did you record any DTCs which begin with a "U" and with a current status?

Go to Step 33

Go to Step 32

32

Did you record any DTCs which do not begin with a "U"?

Go to Step 33

Go to Step 35

33

Diagnose the DTCs as directed by the diagnostic procedures for the particular module or malfunction. Refer to Control Module References in Body Control System for the applicable Diagnostic System Check.

Did you complete the action?

Go to Step 34

--

34

Did you diagnose all of the DTCs?

Go to Step 35

Go to Step 33

35

Use the scan tool in order to clear the DTCs.

Did you complete the action?

System OK

--